1. Field of the Invention
The present invention relates to an outboard motor in which exhaust passage means for discharging exhaust gas of an engine into an exhaust passage of case means is formed by joining an exhaust manifold and an exhaust guide via a joining part.
2. Description of the Related Art
With regard to the structure of an outboard motor engine exhaust system, there is a structure in which a separate exhaust manifold is joined to an exhaust port opening on an outer wall of a cylinder head so as to guide exhaust gas downward, and a structure in which an exhaust port formed within a cylinder head is bent toward a cylinder block, and a downstream part of the exhaust port is connected to an upstream part of an exhaust passage formed within the cylinder block so as to guide exhaust gas downward. Employing the former structure, which includes an exhaust manifold, not only enables the dimensions of the cylinder head and a cylinder block to be reduced, but also makes machining of the exhaust port and an exhaust passage easy (see Japanese Utility Model Registration Publication No. 2568292 and Japanese Patent Application Laid-open No. 10-212948).
However, when exhaust passage means is divided into an exhaust manifold extending along a side face of a cylinder head and an exhaust guide connected to the lower end of the exhaust manifold and extending toward a lower face of the cylinder head in order to make machining of the exhaust passage means easy or improve the ease of assembling the exhaust passage means to the cylinder head on the upstream side and an exhaust passage on the downstream side while absorbing dimensional errors of the exhaust passage means, the dimensions of a joining part increase, leading to a possibility that the joining part might interfere with the side face of the cylinder head. In order to avoid this interference, if the entire exhaust passage means is fixed so as to be separated from the side face of the cylinder head, the layout within a confined engine compartment becomes difficult.